When a turbine rotor is left in a non-rotation state at a high temperature during shutdown of a steam turbine or the like, bending in the turbine rotor may occur due to distortion by heating generated in a turbine rotor due to a temperature difference generated in a turbine casing in association with a decrease in temperature of steam or a gas in the turbine or the weight of the turbine rotor. Here, in order to avoid the occurrence of bending in the turbine rotor used in the steam turbine or the like, during shutdown of the steam turbine and before starting the steam turbine, turning that rotates the turbine rotor for a predetermined time at a low speed should be performed. In order to perform such turning, a turning device configured to rotate the turbine rotor using power of an electric motor is widely used.
In such a turning device, when regular rotation of the turbine rotor starts, in order to prevent the turning device from being overloaded and the turning device from being damaged, a mechanism configured to separate a pinion gear to protect the turning device is provided. Meanwhile, as a backflow or the like of a compressor process gas occurs during turning of the steam turbine or the like, the turbine rotor may be reversely rotated. In this case, the pinion gear cannot be separated, an excessive load is applied to the turning device and the turning device may be damaged.
In order to avoid damaging the turning device, for example, in Patent Literature 1, a one way clutch configured to automatically separate the turning device from the turbine rotor and a one way clutch (a reverse rotation preventing apparatus) configured to prevent (restrict) reverse rotation of the turning device when a rotational speed of the turbine rotor exceeds the rotational speed of the turning device are provided.